Control system



H. 8. JQNES CONTROL SYSTEM Filed June 12, 1942 INVENTOR.

Patented Mar. 28, 1944 CONTROL SYSTEM Harry S. Jones, Washington,

The Brown Instrument Company,

D. 0., asslgnor to Philadelphia,

Pa., a corporation of Pennsylvania Application June 12, 1942, Serial No. 446,830

9 Claims.

The present invention relates to new and useful improvements in light sensitive control systerns, and more particularly, to new and useful improvements in such systems arranged for controlling the operation 01 fuel burners.

It is a general object of the present invention to provide an improved safety control system for a fuel burner which responds in one sense to the presence of a flame at said burner and responds in another sense to the absence of a flame at said burner.

A more specific object of the present invention is to provide an improved safety control system for a fuel burner which utilizes a light sensitive device as the flame responsive element, and perates on failure of the burner flame to ignite when the burner is initially placed in operation or on failure of the flame while the burner is in operation, to shut off the supply of fuel to the burner.

In furnaces or fuel burners of the type which operate on liquid or gaseous fuels, the flame often fails to ignite upon initially placing the burner in operation or becomes extinguished while the burner is in operation for various reasons, and unless some provisions are made for immediately detecting such initial failure of ignition or flame failure and for shutting off the supply of fuel to the burner, a highly explosive mixture of fuel will be permitted to accumulate in the combustion chamber. Permitting such a combustible mixture of fuel to accumulate not only results in a waste of fuel, but also gives rise to a hazardous condition in that the combustible mixture is apt to explode, particularly if an attempt is made to relight the fuel before the combustion chamber has been purged of the explosiv mixture.

It is a particular object of the present invention to provide an improved and simplified safety control system which operates in a positive manpeer to quickly shut oil the supply of fuel to the burner when, for any reason, the fuel burner flame fails to ignite within a predetermined time upon initial placing of the burner into operation, or the burner flame becomes extinguished while the burner is in operation, and also to provide a signal for calling the attention of an attendant to the abnormal shut down of the burner.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however,-its advantages and specific objects obtained with its use,

reference should be made to the accompanying 6? drawing and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

The single figure of the drawing shows a fuel oil burner having a combustion chamber I in which a spray of oil supplied by an oil pumping arrangement indicated generally by the reference character 2 is burned upon being ignited by a gas or other pilot light 3 which usually is continuously burning. The oil pumping equip ment 2 is electrically driven from alternating current supply lines L and U which may be ordinary volt lighting mains, and comprises a unidirectional electrical motor 4 which is adapted to be electrically connected to the supply lines L and L and a fuel pump 5 Which is driven through the medium of belt means by the motor 4. When the motor a is energized, a spray oi. fuel will be supplied by the fuel pump 5 trom a fuel tank indicated in dotted lines and designated by the reference numeral 6 to the combustion chamber l.

The oil pumping equipment 2 is controlled by means of a thermostat l which may be located in a room or space to be heated. The thermostat I may be of any suitable construction and in-= cludes a bimetallic element 8 connected by means of a conductor 9 to the alternating current supply line L and a contact blade iii adapted to engage a relatively stationary contact H which is connected to the supply line L through a thermal switch it and the primary winding iii of a transformer M.

The thermal safety switch it may desirably be or the general type disclosed in Patent 1,958,081, issued to F. S. Denison on May 8, 1934. As illustrated, this switch comprises a stationary arm l5 and a movable arm it biased for movement away from arm. is but normally held in engagement with the latter by means or a bimetallic element i'l. Element i! is rigidly secured at one end to a block 88 and is arranged to be heated by a coil it when the latter is energized through a circuit described hereinafter; Upon energiz ation of coil it for a predetermined period of time, element M will be warped sufficiently in the counterclockwise direction to permit arm I8 acting under spring or other bias to separate from switch arm i5 thereby interrupting the circuit including thermostat l. The switch i2 will remain locked in this position until manual- 15 returned to its normal closed position. When the movable arm i6 is thus released by element ll it moves into engagement with a relatively fixed contact NA and thereby closes an energizing 22. connected by means of a resistor 57 to the point ing circuit to a signalling lamp L from the supply lines L and L The transformer l4 supplies power-to a circuit arrangement to be described which controlsthe operation of the oil pumping equipment 2 under control of the thermostat l and also in accordance with the conditions of combustion of the spray of'fuel'. oil supplied to the chamber I by th pumping equipment 2. The transformer It is a combination step-up and step-down transformer and comprises the-line voltage primary winding l3, low voltage secondary windings 25, 2t and 23 and a high voltage winding 22. Low voltage secondary winding 25 is used to energize the heater filaments 2t and 25 of an electric discharge device 26, and, as shown, is connected to the filaments 25 and 25, which are connected in parallel, by conductors 2i and 28; I

The electric discharge device 26 comprises two sections designated by the reference numerals 25 and 35, respectively, within one envelope. section 29 includes an anode 3! a control electrode 32, a. cathode 33 and the heater filament 25, and the section 30 includes an anode 35, a control electrode 35, a cathode 35 and the heater filament 25. As shown, the cathodes 33 and 35 are directly connected within the envelope 25. The section 25 is utilized as a half wave rectifier while the section 35 is utilized as a triode.

The output circuit of rectifier 29 is energized by the transformer secondary winding 22 through a circuit which may be traced from the lower end of winding 22 through a conductor 37, a conductor 38, a switch arm 39, a contact 55, a conductor M, a winding 52 of a relay 33 across which a condenser 55 is connected, anode 3i, cathode 53, a conductor -55, transformer secondary winding 23, and a conductor 55 to the upper end of wind- As illustrated, control electrode 32 is of connection of conductor i and relay winding 52. Consequently, section 23 is normally fully conductive and relay 53 is normally energized whenever the transformer i5 is energized, which action is efiected by closure of the thermostat switch arm it with the contact H.

The output circuit of triode 39 is energized by The 56', a conductor 55, the cathode of photoelectric cell 50, the anode of cell 50, a conductor 56, and the conductor 3! to the lower terminal of winding 22. The control electrode of triode 35, as previously noted, is connected through resistance 5| to the common terminal ofresistance 53 and conductor 55. The flow or electric current through this circuit is controlled in accordance with the illumination of photoelectric cell 50 and produce a potential drop across resistance 53 and condenser 54 which is of the proper polarity to tend to impress a potential. on the control electrode 35 which is positive with respect to the potential of cathode 35, and thereby tends to render the triode 35 conductive. This potential drop produced across resistance 53 and condenser 54 thus is opposed to the potential impressed between the control electrode 35 and cathode 36 by the transformer secondary winding 23. With this arrangement, therefore, the conductivity of the triode 30 and thereby the energization of relay 39 is adapted to be controlled in accordance with the illumination of photoelectric cell 50.

The photoelectric cell 55 is mounted in any convenient manner outside an opening 5'! in the wall of combustion chamber I, so as to be exposed to lightemanating therefrom. A lens 58 may desirably be provided, as shown,.- so as to concentrate the rays from a large area within the chamher 9 upon the photoelectric cell 50. Preferably light from the flame of the main burner 2 is focused upon the cell 50 so that the latter is rendered conductive when there is a flame at the main burner but is non-conductive when there is the transformer secondary winding 22 through a circuit which may be traced from the lower end of winding 22 through conductors 3i and 35, switch arm 39, contact 50, conductor 5!, a winding 53 of a relay 59, which is shunted by a condenser 59A, anode 35, cathode 55, conductor 55, transformer secondary winding 25, and conductor 55 to the upper end of winding 22.

- The -input circuit of triode 30 includes the transformer secondary winding 25 in one branch and in another branch includes the anode to cathode resistarfce of a photoelectric cell 55. The first mentioned branch may be traced from the 0 control electrode 35 through a resistance 5!, a

conductor 52 in which a resistance 53 shunted by a condenser 55 is inserted, transformer secondary winding 23 and conductor 35 to cathode 35. The winding 23 is so woundon transformer M as to tend to apply a potential on the control electrode 35 which is negative with respect to the cathode 35 during the half cycles whenthe anode 3% is positive. This branch of the input circuit of triode 35, thus, tends to render the triode non-conductive.

The second branch of the input circuit of triode 35 may be traced from the upper terminal of transformer secondary winding 22, conductor 55,

no flame present at the main burner.

Summarizing, when a flame is not present at the main burner the conductivity of photoelectric cell 50 is relatively low and as a result the triode 55 is substantially non-conductive since the potential drop produced across resistance 53 by the flow of current from the photoelectric cell therethrough is then insuificient to offset the effect of the negative potential applied to the control electrode 35 by the transformer'secondary winding 23. When a flame is burning at the main burner 2, however, the conductivityof photoelectric cell 55 is increased and consequently the potential drop across resistance 53 is increased. This increased potential drop across resistance 53 operates to render the triode 30 conductive and thereby effects energization of the relay 59.

For convenience of illustration, the sections 29 and 35 will be referred to as conductive hereinafter when their output current is suflicient to actuate the respective relays 53 and 59 associated therewith, and as non-conductive when their output current is insuificient for that purpose. For further convenience, a contact through which a circuit is completed when a relay is actuated will be designated a front contact of the relay, and a contact through which a circuit is completed when the relay is deefiergized will be designated a back contact 56. The relay 43 comprises the conductor 52, resistance 53 shunted bycondenser winding 42 and switch arms 63 and 59 which cooperate-with front contacts 10 and 7!, respectively. There is also provided a relay it the energization of which is controlled by the relays 53 and 55 and which is utilized for a purpose explained hereinafter. Relay 12 comprises a winding 12A and switch arms 13 and 14 in addition to the switch arm 39 already mentioned. Switch arms 39 and I4 cooperate with back cont acts 40 and 15, respectively, and switch arm 13 cooperates with a front contact 16.

When the temperature of the space to be heated is higher than the desired value, all parts of the system are in the positions shown in Fig.

1, and the supply of fuel to the combustion chamber I is then cut off. If the temperature of the room or space to be heated falls below the value it is desired to maintain, the thermostat l operates to move the switch blade i into engagement with the contact ii. This results in closure of the energizing circuit to the transformer primary winding l3 and thereby effects energization of the transformer secondarywindings. Immediately upon energization of the transformer secondary winding, energizing current is supplied the heater IQ of the thermal safety switch through a circuit which may be traced from the upper terminal of winding 2|, through a conductor 80, a conductor 8|, contact 66, switch arm 60, a conductor 82, and resistance I9 to the lower terminal of winding 2|.

After the cathodes 33 and 36 of the sections 29 and have been heated to their operating temperatures, the rectifier 29 is immediately rendered conductive and energizes the relay 43. The relay 43 then operates switch arm 89 into engagement with contact I! to complete an energizing circuit to the pump motor 1. This chargizing circuit to motor 4 may be traced from the supply line L to a conductor it, switch arm i4, contact 15,, conductor 83, switch arm 69, contact 'li, a conductor 84, motor i, and. a conductor 85 to the supply line L.

Operation of motor 4 causes a spray oioil to v be supplied to the combustion chamber i from the fuel supply tank 6, which spray of oil under normal combustion conditions will be ignited by the flame of the continuously burning pilot light 3. It is noted relay 43 when energized also actuates switch arm 68 into engagement with contact iii.

If the spray of oil supplied to combustion chamber i fails to ignite within a predetermined time, the energizing circuit to the transformer primary winding 93 is opened at the switch i5, t6, the relay 43 is deenergized, and consequently the burner motor 4 is deenergized. This effect is obtained by virtue of the action of the thermal safety switch i 2, the heater it or which, as noted hereinbeiore, is energized immediately upon clo sure of switch blade iii upon contact ii, and causes opening of the switch iii, it when ener glzed for a predetermined time. c

If the main burner ignites properly, the appearance of a flame thereat operates to increase the conductivity of photoelectric cell 59, and thereby operates to render the triode 30 conductive and effects energization of the relay 49 in the manner explained hereinbefore. Relay 49 when energized actuates switch arm 88 into engagement with contact 84 to close an energizing circuit to the pump motor 4 which is independent of the switch arms 69 and 14, moves switch arm 80 out of engagement with contact 68 to deenergize the heater I9 oi the thermal safety switch l2, moves switch arm 59 into engagement with contact 63 to close an energizing circuit to the winding 12A of relay l2, and moves switch arm 62 into engagement with the contact 65 to close an energizing circuit from the transformer secondary winding 22 to the sections 29 and 30 and the relay windings 42 and 48 which is independent of the switch arm 39 and contact 40.

The energizing circuit to the motor 4 closed upon energization of the relay 49 may be traced relay 12 which is closed upon energization oi relay 49 may be traced from the upper end of winding 2| to conductor 80, switch arm 68, contact 70, switch arm 59, contact 63, winding 12A, and a conductor 88 to the lower terminal of winding 2|.

The auxiliary energizing circuit to the sections 23 and 30 and the relay windings 42 and 48 which is closed upon energization of relay 49 is effected by closure of the switch arm 62 on the contact 85, which switch arm and contact shunt the switch arm 38 and contact 40. Subsequent movement of switch arm 39 out of engagement with contact 40, therefore, does not result in opening or the energizing circuit from the transformer secondary winding 22 to the triodes 29 and 33 and the relay windings Q2 and 48. To this end the relay i2 is preferably so designed as to be slower in operation than the relay 49 to thereby guard against the switch arm. 39 being moved out of engagement with contact 40 before the contact 62 is moved into engagement with the contact 85. Relay it when energized closes a holding cir-. cuit for itself, moves the switch arm 39 out oi engagement with the contact at, and moves the switch arm it out of engagement with the contact E5. The holding circuit which is closed upon energization oi. relay it may be traced from the upper terminal of winding H to conductor 80, conductor 6i, switch arm 13, contact '16, a conductor 87!, winding WA and conductor 86 to the lower terminal of winding 2i.

The fuel burner system is now in :full operation and normally a spray or" fuel will continue to be supplied to the chamber i as long as the thermostat 7 calls for heat, or more specifically, as long as the switch arm iii and contact ii are held in engagement.

If the flame at the main burner should become extinguished for any reason the relay 39 will be deenergized immediately, or after any de. sired time delay which can be predetermined by properly choosing the value of condenser dd. Deenergiaztion of relay it? causes the switch arms t9, t2 and hi to $3, and 64%, respectively, and causes switch arm E8 to move into engagement with contact to. fieparation of switch arm 92 and contact 65 opens the enercizing circuit from the transformer secondary winding 22 to the tube sections 29 and 3t) and the relay windings 42 and 18. Separation of switch arrn Hi from contact 84 deenerglzes the pump motor 4 which cannot again become energized because the relay 49 is locked out by separation of its own switch arm 82 from the contact 65 and the switch arm 39 is held away from the contact 40 by the then energized relay l2. Engagement of the switch arm 89 with the con, tact B6 closes an energizing circuit to the heater it of the thermal safety switch and after a predetermined time the thermal safety switch i2 looks out and completely deenergizes the system. The thermal safety switch I2 must be manually separate from contacts reset after the abnormal condition causing the flame to become extinguished has become corrected before the burner can again become ignited.

Such energization of the heater IQ of the thermal safety switch I? not onl causes deenergization of the system but also efiects energization of the signalling lamp L to thereby visually indicate to an attendant the abnormal burner shut down. The circuit through which lamp'L is energized may be traced from supply line L to lamp L, contact lliA of the thermal safety switch, and switch arm It to the supply line L Recapitulating, when the burner operates nor-' mally, the thermostat 'l controls the operatic:

Eac

of the burner automatically at all times. time the thermostat 7 calls for heat there is a delay in energizing the burner motor 6, which delay is determined by the time required for the heaters 25 and 25 of the electronic discharge device 26 to come to their normal operating temperature. permanently locked out as described above if the burner is not ignited within a predetermined time after the burner motor 4 is energized. In addition, the entire-system is shut down and permanently locked out if the flame should become extinguished while the burner is in operation.

In either case the system cannot 'again be started means may also be provided for indicating the abnormal burner shut-down.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of my invention now known to me, it will be apparent to those skilled in the form of the apparatus disclosed without departing from the art that changes may be made in the spirit of my invention as set forth in the appended claims, and that certain features of my invention may sometimes be used to advantage without a corres onding use of other features.

aving now described my invention, what I claim as new and desire to secure by Letters Patentis:

1. In an oil burning system, electrically operated means for projecting fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means'including a source of electrical current, a connection between said source of current and said electrically operated means, said connection having a normally closed contact and a normally open contact connected in series therein and it nor- The entire system is shut down and mally open contact connected in shunt to said first and second mentioned contacts, a relay coil associated with said first mentioned contact and adapted when energized to open said contact, a

second normally closed contact and a normally open contact associated with said relay coil, said ing fuel, a connection between said source oi current and said transformer primary winding including said switching means, a connection including one of said transformer secondary windings and said relay coil and having two normally open contacts connected in series therein and the normally open contact associated with said relay coil connected in shunt to said series connected contacts, a relay coil associated with said second mentioned contact and with one of the normally open series connected contacts in said last mentioned connection and adapted when energized to close both of said contacts, a connection between said second mentioned relay coil and another of said transformer secondary windings to energize said second mentioned relay coil tothereby close said second mentioned contact to efiect energizationoi' said electrically operated means when the temperature of said space is lower than the desired value, a third relay coil associated with said thind mentioned contact and with the second normally open series contact in the connection including the first mentioned relay and adapted whenenergized to close both of said contacts, a third normally open contact associated with said third mentioned relay coil and adapted to be closed when said relay is energized, a light sensitive device responsive to the burning of the fuel, an electronic discharge device having an input circuit controlled by said light sensitive device and an output circuit, a connection including one of said transformer secondary windings, said last mentioned contact and the second mentioned normally closed contact'associated with said first mentioned relay in parallel, said third mentioned relay, and the output circuit of said electronic discharge device whereby energization of said third relay coil efiects energization of said first mentioned relay coil, and additional means controlled by said third mentioned relay coil and disposed in the connection between said source and the transformer, primariy winding to deenergize the latter and thereby the 'entire system upon the occurrence of said third mentioned relay coil being deenergized a predetermined time while said transformer primary winding is energized.

2. In an oil burning system, electrically oper-- ated means for projecting fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means in-- cluding a source of electrical current, a connection between said source of current and said electrically operated means, said connection having a normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned contacts, a relay coil associated with said first mentioned contact and adapted when energized to open said contact, a second normally closed contact and a normally open contact associated with said relay coil, said last mentioned normally closed contact being adapted to be open and said last mentioned normally open contact being adapted to be closed when said relay coil is energized, a transformer having a prilast mentioned normally closed contact being adapted to be opened and said last mentioned normally open contact being adapted to be closed when said relay coil is energized, a transformer having a primary winding and a plurality of secondary windings, switching means responsive to the temperature of a space heated by the burnt mary winding and a plurality of secondary windings, switching means responsive to the temperature of a space heated by the burning fuel, a connection between said'source of current and said transformer primary winding including said switching means, a connection including one of said transformer secondary windings and said relay coil and having two normally open contacts connected in series therein and the normally open contact associated with said relay coil connected in shunt to said series connected contacts, a relay coil associated with said second mentioned contact and with one of the normally open series connected contacts in said last mentioned connection and adapted when energized to close both of said contacts, a connection between'said sec ond mentioned relay coil and another of said transformer secondary windings to energize said second mentioned relay coil, a third relay coil associated with said third mentioned contact and with the second normally open series connected contact in the connection including the first mentioned relay and adapted when energized to close both of said contacts, a third normally open contact associated with said third relay coil and adapted to be closed when said relay is energized, a light sensitive device responsive to the burning of the fuel, an electronic discharge device having an input circuit controlled by said light sensitive device and an output circuit, and a connection including one of said transformer secondary windings, said last mentioned contact and the second mentioned normally closed contact asso= ciated with said first mentioned relay in parallel, said third mentioned relay, and the output circuit of said electronic discharge device.

3. In an oil burning system, electrically operated means for projecting fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means including a source of electrical current, a connection between said source of current and said electrically operated means, said connection having a normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned contacts, a relay coil associated with said first mentioned contact and adapted when energized to open said contact, a second normally closed contact and a second normally open contact associated with said relay coil, said last mentioned normally closed contact being adapted to he opened and said last mentioned normally open contact being adapted to be closed when said relay coil is energized, a transformer having a primary winding and a plurality of secondary windings, switching means responsive to the temperature of a space heated by the burning fuel, a connection between said source of current and said transformer primary winding including said switching means, a connection including one of said transformer secondary windings and said relay coil and having two normally open contacts connected in series therein and the normally open contact associated with said relay coil connected in shunt to said series connected contacts, a relay coil associated with said second mentioned contact and with one of the normally open series connected contacts in said last mentioned connection and adapted when energized to close both of said contacts, a connection between said second mentioned relay coil and another of said transformer secondary windings to energize said second mentioned relay coil, a third relay coil associated with said third mentioned contact and with the second normally open series connected contact in the connection including the first mentioned relay and adapted when energized to close both of said contacts, a third normally open contact associated with said third re- ,lay coil and adapted to be closed when said relay is energized, a device responsive to the burning of the fuel, an electronic discharge device having an input circuit controlled by said device and 76- an output circuit, a circuit connection including one of said transformer secondary windings, said last mentioned contact and the second mentioned normally closed contact associated with said first mentioned relay in parallel, said third mentioned relay, and the output circuit of said electronic discharge device.

4. In an oil bur ring system, electrically operated means for projecting fuel into a zone of igni tion, means for igniting the fuel, means for controlling said electrically operated means including a source of electrical current, a connection between said source of current and said electrically operated means, said connection having 9. normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned contacts, a relay coil associated with said first mentioned contact and adapted when energized to open said contact, a second normally closed contact and a second normally open contact associated with said relay coil, said last mentioned normally closed contact being adapted to be opened and said last mentioned normally open contact being adapted to he closed when said relay coil is energized, a transformer having a primary winding and a plurality of secondary windings, switching means responsive to the temperature of a space heated by the burning fuel, a connection between said source of current and said transformer primary winding including said switching means, a connection including one of said transformer secondary windings and said relay coil and having two normally open contacts connected in series therein and the normally open contact associated with said relay coil connected in shunt to said series connected contacts, a relay coil associated with said second mentioned contact and with one of the normally open series connected contacts in said last mentioned circuit connection and adapted when energized to close both of said contacts, a connection between said second mentioned relay coil and another of said transformer secondary windings to energize said second mentioned relay coil, a third relay coil associated with said third mentioned contact and with the second normally open series connected contact in the connection including the first mentioned relay and adapted when energized to close both of said contacts, a third normally open contact associated with said third relay coil and adapted to be closed when said relay is energized, and a circuit connection including one of said transformer secondary windings, said last mentioned contact and the second mentioned normally closed contact in parallel, said third mentioned relay, and means including a device responsive to burning of the fuel to control the conductivity of said last mentioned connection.

5. In an oil burning system, electrically operated means for projecting fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means including a source of electrical current, a circuit connection Between said source of current and said electrically operated means, said circuit connection having a normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned contacts, means responsive to the temperature of a space heated by the burning fuel to close said second mentioned contact to effect energization of said electrically operated means when the temperature of said space is lower than the desired value, means actuated in response to burning of the fuel, and means controlled joint ly by said last mentioned means and by said temperature responsive means to open said first mentioned contact and to close said third men= tioned contact and operative upon abnormal extinguishment of the burning fuel to open said third mentioned contact and to maintain said first mentioned contact open to thereby deener= gize said electrically operated means.

6. In an oil burning system, electrically oper-. ated means for projecting, fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means including a source of electrical current, a circuit connection between said source of current and said electrically operated means, said circuit connection having a normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned contacts, means responsive to the temperature of a space heated by the burning fuel to close said second mentioned contact to efiect energization of said electrically operated means when the temperature of said space is lower than the desired value, light sensitive means actuated in response to burning of the fuel, means Jointly controlled by said light sensitive means and by said temperature responsive means to open said first mentioned contact and to close said third contact,

7. In anoil burning system, electrically operated means for projecting fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means including a source of electrical current, a circuit connection between said source of current and said electrically operated means, said circuit connection having a normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned con= tacts, means responsive to the temperature of a space heated by the burning fuel to close said second mentioned contact to effect energization of said electrically operated means when the temperatureof said space is lower than the desired value, means actuated in response to burning of the fuel, means jointly controlled by said last mentioned means and by said temperature responsive means to open said first mentioned contact and to close said third mentioned con- (iii aseaaaa tact, said last mentioned means being operative upon abnormal extinishment of the burning fuel to open said third mentioned contact and to maintain said first mentioned contact open to thereby deenergize said electrically operated means and operative thereafter to open said second mentioned contact irrespective of the condition of said temperature responsive means and to close said first mentioned contact.

8. In an oil burning system, electrically operated means for projecting fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means including a source of electrical current, a circuit connection between said source of current and said electrically operated means, said circuit connection having a normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned contacts, means responsive to the temperatureof a space heated by the burning fuel to close said second mentioned contact to effect energization of said electrically. operated means when the temperature of said space is lower than the de-' sired value, means responsiveto burning of the fuel, and means controlled by said last mentioned means to close said normally opened contact and to open said normally'closed contact and operative to hold the latter in said opened position independently of said responsive means and operative upon failure of the fuel to burn to open both of said normally open contacts to deenergize said electrically operated means.

9. In an oil burning system, electrically operated means for projecting fuel into a zone of ignition, means for igniting the fuel, means for controlling said electrically operated means including a source of electricalcurrent, a circuit connection between said source of current and said electrically operated means, said circuit connection having a normally closed contact and a normally open contact connected in series therein and a normally open contact connected in shunt to said first and second mentioned contacts, means responsive to the temperature of a space heated by the burning fuel to close said second mentioned contact to effect energization of said electrically operated means when the temperature of said space is lower than the desired value, light sensitive means responsive to burning of the fuel, and means controlled by 

